The present invention relates to a liquid ejection apparatus which can eject liquid droplets of different sizes from the same nozzle, and more particularly to a liquid ejection apparatus which can eject plural liquid droplets in one ejection period.
A liquid ejection apparatus is used in various apparatuses such as: a recording device which is useful in an image recording apparatus; a color material spraying apparatus which is useful in the production of a color filter for a liquid crystal display device; an electrode material (electrically conductive paste) spraying apparatus which is useful in the formation of electrodes in an organic EL display device, an FED (surface light emitting display device), or the like; a bio-organic substance spraying apparatus which is useful in the production of biochips, and a sample spraying apparatus serving as a precision pipette. An ink jet recording apparatus will be described as an example of a liquid ejection apparatus.
As an output apparatus for a computer, recently, a color ink jet printer in which inks of several colors are ejected from a print head is widely used for printing an image processed by a computer in multi-color and multi-gray scale levels.
An ink jet printer has a print head in which many nozzles are arranged in a sub-scanning direction (sheet feeding direction). The print head is moved in a main scanning direction by a carriage mechanism, and a sheet is fed by a predetermined degree in the sub-scanning direction, thereby obtaining a desired print result. Based on a dot pattern data which is obtained by expanding a print data supplied from a host computer, ink droplets are ejected at respective predetermined timings from the nozzles of the print head, and the ink droplets impact a print recording medium such as a recording sheet to adhere therewith, whereby a printing process is conducted. As described above, in an ink jet printer, it is controlled whether ink droplets are ejected or not, i.e., a dot on/off control is conducted. When no countermeasure is taken, therefore, an intermediate gray scale such as gray cannot be printed out.
Recently, an ink jet printer is therefore used in which plural liquid droplets of different weights are ejected from the same nozzle to variably control the diameter of a recording dot. In a first related ink jet printer, for example, a common waveform generating device generates plural driving voltage waveforms corresponding to ink ejection amounts, one of the driving voltage waveforms is selected in accordance with a gray-scale data signal, and the selected driving voltage waveform is applied to a piezoelectric element (see JP-A-9-11457).
In a second related ink jet printer, by contrast, a driving signal which is output in each print period is configured by plural driving pulses, one or more of the driving pulses are time-divisionally selected by a print data having pulse selecting signals respectively corresponding to the driving pulses, and the selected driving pulses are applied to a piezoelectric element (see JP-A-10-81013).
In the first related example, analog switches of a transmission gate (hereinafter, referred to simply as TG) in a print head are required in a number which is equal to the product of the number of the driving voltage waveforms x that of nozzles. Therefore, an integrated circuit (hereinafter, referred to simply as IC) in which the TG is formed is inevitably increased in size. As a result, also the size of a print head is enlarged, and the production cost is raised.
In the second related example, the driving signal which is output in each print period is configured by plural driving pulses, one or more of the driving pulses are time-divisionally selected, and the selected driving pulses are applied to the piezoelectric element. Therefore, a head is hardly driven in accordance with a high frequency.